Biobased films from amphiphilic lignin-graft-PLGA copolymer

Authors: MENDEZ, OMAR - Louisiana State University; ASTETE, CARLOS - Louisiana State University; HERMANOVÁ, SONA - Mendel University; BOLDOR, DORIN - Louisiana State University; Orts, William; SABLIOV, CRISTINA - Louisiana State University

Submitted to: BioResources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2023
Publication Date: 7/17/2023
Citation: Mendez, O.E., Astete, C.E., Hermanová, S., Boldor, D., Orts, W.J., Sabliov, C.M. 2023. Biobased films from amphiphilic lignin-graft-PLGA copolymer. BioResources. 18(3):5887-5907. https://doi.org/10.15376/biores.18.3.5887-5907.
DOI: https://doi.org/10.15376/biores.18.3.5887-5907

Interpretive Summary: Surfactants are also known as surface-active agents, are used in a wide range of applications due to their ability to reduce surface tension between liquids and solids. Commercially, they are used as laundry detergents, soaps, wetting agents, emulsifiers, foaming agents, and dispersants in homecare products. Common uses include cleaning products, personal care items, and even in industrial applications like agriculture and oil recovery. Most surfactants are amphiphilic copolymers, molecules having both hydrophobic (nonpolar oil-attractive) and hydrophilic (polar water-attractive) regions. The cleansing properties of a soap or detergent require the molecule to have both a hydrophobic and hydrophilic regions to interact with both oil and water phases. Amphiphilic copolymers were synthesized by grafting poly(lactic-co-glycolic) acid with two lignin types: alkaline lignin and lignosulfonate, and films were created. Films presented one side as being more hydrophobic (O-side) and smoother, and the second side more polar and with an uneven surface (W-side). Contact angle of water on the W-side was lower than the O-side corresponding to a higher lignin content and influenced by the lignin type (alkaline < lignosulfonate) and lignin: PLGA ratio. X-ray photoelectric spectroscopy analysis showed higher percentages of sulfur on the W-side, which supports a preferential partitioning of the lignin. Tensile testing demonstrated the significant impact of lignin type on the mechanical properties of the films. Alkaline films showed a higher maximum strength, a higher stiffness, and a higher tensile strength at the elastic limit compared to lignosulfonate films. However, for lignosulfonate films, ductility at break point was 4-fold higher than that of alkaline films.

Technical Abstract: Amphiphilic copolymers were synthesized by grafting poly(lactic-co-glycolic) acid with two lignin types: alkaline lignin and lignosulfonate. An interphase formation technique was used to produce films based on the copolymers. Films presented one side as being more hydrophobic (O-side) and smoother, and the second side more polar and with an uneven surface (W-side). Contact angle of water on the W-side was lower than the O-side corresponding to a higher lignin content and influenced by the lignin type (alkaline < lignosulfonate) and lignin: PLGA ratio. X-ray photoelectric spectroscopy analysis showed higher percentages of sulfur on the W-side, which supports a preferential partitioning of the lignin. Tensile testing demonstrated the significant impact of lignin type on the mechanical properties of the films. Alkaline films showed a higher maximum strength, a higher stiffness, and a higher tensile strength at the elastic limit compared to lignosulfonate films. However, for lignosulfonate films, ductility at break point was 4-fold higher than that of alkaline films.